As it is known, many pourable food products, such as fruit juice, milk, tomato sauce, and beverages in general, are sold in a wide range of containers of different types and sizes, such as: parallelepiped-shaped packages made of multilayer, plastic- and/or paper-based, laminated materials or so-called multilayer cardboard materials; beaker-shaped plastic packages; blow-molded bottles; or glass, sheet metal or aluminium containers.
All these containers are fitted with closures which can be opened to allow access by the consumer to the food product, either to pour it into a drinking vessel or consume it straight from the container.
Screw cap closures are commonly used on bottle-type containers, whereas containers made of multilayer cardboard materials are often simply provided with tear-off markers, or with pour openings formed in the containers and covered with pull tabs.
Containers made of multilayer cardboard materials are also known to be fitted with plastic closures injection molded directly onto the containers, about openings formed through the packaging material, so as to completely close and seal the openings. Closures of this sort normally define the pour opening of the container, which may be fitted, for example, with a screw or snap cap.
Injection molded closures may of course be of various sizes and even define the whole top of the container, as in the case of the container known by the registered trademark “Tetra Top”, and the top of which is illustrated in Patent Application EP-A-0965531.
Though permitting precise, high-quality forming, injection molding container tops does not allow for integrating a layer of gas-barrier material in the tops, as required, for example, when packaging vitamin-supplemented fruit juice.
As described, for example, in Patent EP-B-1197438 and Patent Application WO 03/061940, plastic tops of containers are also known to be produced by blowing a plastic tubular preform, which may include a layer of gas- and also light-barrier material.
The container known by the trademark “Tetra Aptiva” is one example of a container produced using this technique, i.e. having a main bottom portion made of multilayer cardboard material, and a top, for pouring the liquid or pourable product in the container, produced by blowing a plastic tubular preform.
This technique provides for a high degree of forming precision, especially as regards the pour opening, but has the drawback of requiring the use of special-purpose equipment.
To produce plastic tops or closures to be applied to the container portion of multilayer cardboard material, a method has recently been devised comprising thermoforming and injection molding operations, but no blowing.
One example of this method is described in Patent Application WO 2005/044538, and comprises the step of thermoforming a sheet body of multilayer plastic material having a layer of gas-barrier material, e.g. EVOH. The body is defined integrally by an annular base portion, which is eventually fitted to the cardboard bottom portion of the container, and by a cylindrical neck portion projecting from the inner edge of the base portion and defining, with the base portion, a pour opening by which to pour out the food product. Since thermoforming is performed starting from a sheet of plastic material, the neck portion is closed at its side opposite to the base portion. A protective outer layer of plastic material, with a lateral thread to screw on a cap, is injection molded onto the sheet body so as to form a pouring spout for the container.
After the above operations, and before applying the cap, the material closing the pour opening is removed.
In order to achieve a gas-tight closure of the resulting pouring spout after filling the container, an aluminum foil is welded to the top edge of the spout. After this operation, the cap is finally screwed on the pouring spout.
The above method of producing plastic tops or closures for combined cardboard-plastic containers mainly has the drawback of involving a good deal of time, work, and waste in costly material.
In fact, the portion of material closing the pour opening after the thermoforming operation, and which is removed before applying the cap, normally amounts to about 15-20% of the starting material and, in addition, has a considerable cost as, differently from commonly used plastic materials such as polyethylene or polypropylene, it contains a gas-barrier layer.
Moreover, the aluminum foil welded to the top edge of the pouring spout to achieve a gas-tight closure constitutes a costly additional member, which must be produced and fitted to the spout before the cap is applied to the container.
Furthermore, the resulting closure requires an annoying two-steps operation by the user to obtain the first unsealing. In fact, it is necessary first to unscrew the cap from the pouring spout and then to tear off the aluminum foil covering the spout to reach the content.